Mobile cellular telephones, or mobile stations, are occasionally unable to receive incoming calls because the cellular telephone is camped on a channel or communicating in a network that is different than the network indicated in the registration at the Home Location Register (HLR). The discrepancy results in transmitting pages for the mobile station to the wrong channel or network. A mobile station in this state is sometimes referred to as a “Lost Mobile”.
One such circumstance that may result in the Lost Mobile state is a multi-infrastructure registration race. This circumstance is known to occur when a mobile station, initially registered on a CDMA cellular network, registers on an AMPS cellular network and then returns to the CDMA network in a relatively short time period. The mobile station may register with the AMPS network, for example, upon losing the CDMA paging channel. An analog switch in the AMPS network generally provides the mobile station with an acknowledgement (ACK) before the switch communicates the registration to the HLR. In some instances, when the mobile station returns to and registers with the CDMA network, the CDMA controller switch will communicate the registration on the CDMA network to the HLR before the HLR receives the prior registration from the AMPS switch. Under these circumstances, the mobile station will be camped on the CDMA network, but the HLR will indicate that the mobile station is in the AMPS network, since the HLR receives the AMPS registration after receipt of the CDMA registration. Incoming pages will thus be sent to the wrong network. The delay in the communication of the registration from the AMPS switch to the HLR may be attributed, among other causes, to efforts to reduce network traffic in the AMPS network by accumulating multiple registrations before communicating with the HLR within a timeout period, the expiration of which generally prompts transmission of the registration to the HLR with or without other registrations.
The Lost Mobile state may also result from the failure of a mobile station to receive an acknowledgement upon registering in an AMPS analog network, for example, due to poor coverage, after having been registered in a CDMA network. If the mobile station subsequently returns, from the AMPS network, back to the CDMA network to which it was last successfully registered, the mobile station will not re-register with the CDMA network, since the mobile station will not have been informed of the intervening registration on the AMPS network for its failure to receive the AMPS registration acknowledgement. Under these circumstances, the mobile station will be camped on the CDMA network, while the HLR indicates that the mobile station is in the AMPS network. Incoming pages for the mobile station will again be sent to the wrong network.
A mobile station will generally remain in the Lost Mobile state until any one of several actions occurs, including, among others, the origination of an outgoing communication by the mobile station, re-registration of the mobile station on another system, for example, in response to loss of the paging channel, power-cycling of the mobile station, and/or until the occurrence of a timer-based registration event, which may not occur for 10s of minutes in some networks.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below.